1. Metal Casting
- by MANIGANDAN

2. Introduction:
Metal Casting is one of the oldest materials shaping methods known. Casting means pouring molten metal into a mold with a cavity of the shape to be made, and allowing it to solidify. When solidified, the desired metal object is taken out from the mold either by breaking the mold or taking the mold apart. The solidified object is called the casting. By this process, intricate parts can be given strength and rigidity frequently not obtainable by any other manufacturing process.  The mold, into which the metal is poured, is made of some heat resisting material. Sand is most often used as it resists the high temperature of the molten metal. Permanent molds of metal can also be used to cast products.

5. Melting and Pouring:
Several types of furnaces are available for melting metals and their selection depends on the type of metal, the maximum temperature required and the rate and the mode of molten metal delivery.
Before pouring provisions are made for the escape of dissolved gases. The gating system should be designed to minimize the turbulent flow and erosion of mould cavity.The other important factors are the pouring temperature and the pouring rate.

6. Solidification and Cooling:
The properties of the casting significantly depends on the solidification time cooing rate.
Shrinkage of casting, during cooling of solidified metal should not be restrained by the mould material, otherwise internal stresses may develop and form cracks in casting.
Proper care should be taken at the design stage of casting so that shrinkage can occur without casting defects.

7. Removal, Cleaning, Finishing and Inspection:
After the casting is removed from the mould it is thoroughly cleaned and the excess material usually along the parting line and the place where the molten metal was poured, is removed using a potable grinder.
White light inspection, pressure test, magnetic particle inspection, radiographic test, ultrasonic inspection etc. are used

8. Schematic diagram of casting mould:

9. Steps involved in making a casting:
Make the pattern out of Wood , Metal or Plastic.
Prepare the necessary sand mixtures for mould and core making.
Prepare the Mould and necessary Cores.
Melt the metal/alloy to be cast.
Pour the molten metal/alloy into mould and remove the casting from the mould after the metal solidifies.
Clean and finish the casting.
Test and inspect the casting.
Remove the defects, if any.
Relieve the casting stresses by Heat Treatment.
Again inspect the casting.
The casting is ready for shipping.

10. Advantages of metal casting:
Casting is one of the most versatile manufacturing process.
Casting provides the greatest freedom of design in terms of shape, size and the product quantity.
Casting imparts uniform directional properties and better vibration capacity to the cast parts.
A product may be cast as one piece, there by eliminating the need of metal joining processes.

11. Limitations of casting:
Dimensional accuracy and surface finish of the castings made by sand casting processes are a limitation to this technique.
Many new casting processes have been developed which can take into consideration the aspects of dimensional accuracy and surface finish.
Some of these processes are die casting process, investment casting process, vacuum-sealed molding process, and shell molding process.
The metal casting process is a labor intensive process

12. Applications of Casting:
Transportation vehicles
Turbine vanes
Power generators
Railway crossings
Agricultural parts
Aircraft jet engine parts
Sanitary fittings

13. Different Sections in Foundry:
Pattern making
Sand mixing & preparation
Mould and core making
Mould assembly & handling
Melting
Pouring
Shaking out
Fettling & finishing
Heat treatment
Inspection & testing

14. Metals and alloys commonly used in Foundries:
1. Ferrous
2. Non-Ferrous
FERROUS:
Cast irons
Steels
NON-FERROUS:
Copper alloys
Aluminium alloys
Magnesium alloys
Zinc alloys
Nickel alloys

15. Fuels for Melting Metals:
Coal
Coke
Gas
Oil
electricity

16. Fig: Single piece pattern

17. Fig: split piece pattern

18. Fig: Match plate pattern

19. Fig: Cope and drag pattern

20. 2 types of moulding flask designs

21. Sand mold - opened

22. Sand mold - closed

23. Mixing moulding sand with binders & adhesives

24. Filling sand in moulding flasks

25. Melting furnace

26. Pouring molten liquid

27. Knock out

28. Heat treatment

29. Machining

30. final products of casting

31. Reference: http://nptel.iitm.ac.in/
A text book of Production Technology Vol. I / O.P. Khanna / Dhanpat Rai Publications
A text book of Production Technology (Manufacturing Processes) / P. C. Sharma / S. Chand & Company Ltd
Manufacturing Technology (Second Edition) / P N Rao / Tata McGraw-Hill Publishing Company Ltd
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32. Thank you...